1. Field of the Invention
The present invention relates to a dimming control circuit. More particularly, the present invention relates to a LED dimming control circuit.
2. Description of the Related Art
FIG. 1 is a circuit diagram showing a conventional LED dimming control circuit 100. In the example shown in FIG. 1, the LED dimming control circuit 100 is implemented by a boost-type voltage converter which converts an input voltage Vin1 into an output voltage Vo1, so as to drive a LED 19. A switching control circuit 10 comprises a capacitor C11, a resistor R11, a comparator 13, an oscillating circuit 14, a current-to-voltage converter 15, a latch 16, a current sensing circuit 17, and a driving circuit 18. The connection point of the resistor R12 and the cathode terminal of the LED 19 is used to provide a feedback signal Vfb1. The switching control circuit 10 is used to control the transistor T1 in response to a dimming control signal CN1, the feedback signal Vfb1, and the current of the inductor L1. The user can adjust the brightness of the LED 19 by changing the dimming control signal CN1. The error amplifier 12 compares the reference voltage Vr1 and the feedback signal Vfb1 so as to generate an output current Ieo1 to the switching control circuit 10. When the dimming control signal CN1 is at a high level, the LED dimming control circuit 100 operates in a normal boost-type mode. The peak current value of the inductor L1 is controlled by the output current Ieo1. When the dimming control signal CN1 is at a low level, the LED dimming control circuit 100 stops switching. The decrease of the output voltage Vo1 results in the decrease of the feedback signal Vfb1 and the increase of the output current Ieo1. When the dimming control signal CN1 changes from the low level to the high level, the inrush current of the inductor L1 will be large, resulting in a higher output voltage Vo1 than expected.